The present invention relates to an optical playback head and an optical playback head combined with a magnetic recording head used in magneto-optical recording.
FIG. 1 shows an example of a prior art optical head for a magneto-optical disk. Referring to the figure, reference numeral 1 denotes a magneto-optical disk as a recording medium and 2 denotes a laser beam source. A beam of light from the laser beam source 2 is passed through a grating 3, lens system 4, polarizer 5, beam splitter 6, and an objective lens 7 to be converged on the magneto-optical recording disk 1. The return light beam reflected from the magneto-optical disk 1 is reflected by the beam splitter 6 into a direction at an angle of 90.degree. with its original course, passed through a halfwave plate 8, and subjected to differential detection by means of a polarization beam splitter 9 and photodiodes 10, 11 so that a playback signal is obtained. Meanwhile, reference numerals 12 and 13 denote cylindrical lenses.
Recently, there has been proposed a magneto-optical recording system recording a signal by a magetic-field modulation method and capable of real-time overwriting using a single layer beam. That is, while a recording laser beam 18 is applied to one side of a magneto-optical disk 1 made up of a transparent substrate 15, a magneto-optical recording layer 16, and a protecting layer 17 as shown in FIG. 2, a magnetic head 21 mounted on a slider similar to a head for a magnetic disk is disposed to face to the side of the disk opposite to the side irradiated by the beam, and a signal to be recorded is supplied to the magnetic head 21. Playback is performed with a laser beam in the manner as described with reference to the optical head in FIG. 1.
As an optical head for recording and playback, there is also proposed one using a branch type optical waveguide, in which the end of one branch waveguide is provided with a semiconductor laser as a light source, the end of the other branch waveguide is provided with a photodetector, and the end of the common waveguide is arranged to confront a recording medium, so that an emitted light beam from the semiconductor laser is led through one branch waveguide and the common waveguide to impinge on the recording medium and the reflected beam from the recording medium is guided from the end of the common waveguide to the other branch waveguide and allowed to enter the photodetector, and thereby, a playback signal is obtained (refer to Japanese laid-open Patent Publication Nos. 60-59547, 60-59548, and 61-66238). Further, such an optical head is also known which has a semiconductor laser and photodetectors, disposed at both sides thereof, integrally formed on a substrate, in which a light beam emitted from the semiconductor laser is applied to a recording medium and the reflected light therefrom is received by the photodetectors at both sides (refer to Japanese laid-open Patent Publication No. 62-192032).
In a magneto-optical recording system of a magnetic-field modulation method as shown in FIG. 1 using an optical head arrangement shown in FIG. 2 and a magnetic head 21 of a slider form, it is required that the objective lens 7 for converging the laser beam and the magnetic head 21 must be driven at the same time, and therefore, the mechanism becomes complex, making high-speed access difficult.
Meanwhile, in a magnetic disk system using a thin-film magnetic head today, high-speed access (20 ms) is achieved because a light-weight head is fabricated by application of a technique such as thin-film forming or photolithography to a light-weight slider. However, the track density is limited to a maximum of 3000 TPI chiefly because of difficulty in connection with the signal level at the time of playback.